“PAA- that’s not fair at all. 1,000 years ago, the people who believed in fairies were wrong, and we know that now. People who believe in fairies today are not just wrong, but stupid. Same case here. Someone who made an incorrect hashkafic calculation generations ago was wrong. Now that they have been wrong for years, for you to agree with them is like believing in fairies, in that both are stupid.”
First of all, would you say the same thing about sheidim as you said about fairies?
Second of all, there is a difference between heretical and stupid. Perhaps what you mean to say is that 1000 years ago people were accidentally heretics whereas today they are knowingly heretics. But even if that was what you meant, how could you KNOW now that they were wrong? For the same price, as saying other Rishonim were wrong, you could say the Rambam was wrong.